J.P. Gupta

A model for transitional breakage probability of droplets in agitated lean liquid-liquid dispersions

Abstract A model for transitional breakage probability of droplets in agitated lean fiquid-liquid dispersions is proposed based on the mechanism of breakage of droplets due to their oscillations resulting from relative velocity fluctuations. A universal transitional breakage probability in terms of non-dimensionalized drop diameter is derived for all dispersed phases whose density and viscosity are almost the same as that of continuous phase. The maximum stable drop diameter ds derived from the model, shows a dependence of NWe−0.6. It is shown that a “power law” approximation Kvn is valid for transitional breakage probability for d/ds up to 2. The exponent 2.67, predicted by this model corresponds rather well with an estimate of 2, obtained from experimental observations. A functional relation for the rate constant K in terms of the parameters and physical properties of the system is derived. A universal non-dimensionalized equilibrium drop-size distribution for agitated lean liquid-liquid dispersions is derived by analytical solution of a population balance equation simplified by order of magnitude estimates. Interestingly enough, this analytical solution is the same as the Gaussian distribution suggested empirically by Chen and Middleman.

Thermal and fluid flow effects during solidification in a rectangular enclosure

Abstract An analysis is carried out for the solidification in a rectangular enclosure whose top and bottom surfaces are kept adiabaticand sides are kept at a constant temperature. The transient effects of solidification accompanied by natural convection have been studied in detail. The governing equations are written for the temperature, vorticity, stream function and velocity in the melt along with the heat conduction equations through the solid and the mold. The non-linear coupled equations have been non-dimensionalized and solved with the aid of the Alternating Direction Implicit finite difference method. The velocity profiles in the melt, and the temperature distribution in the melt, the solid and the mold are shown. Isotherms and streamlines in the melt are plotted for different Rayleigh numbers. The dependence of the melt-solid interface movement upon various non-dimensional parameters, such as Rayleigh number (5 × 10 2 −5/s 10 5 Prandtl number (0.1–100), aspect ratio (1.1–5.5), Stefan number (0.5–10) and a parameter indicating the effect of superheat (0.67–2.33) are also studied.

Site security for chemical process industries

Chemical process industries such as oil refineries, fertiliser plants, petrochemical plants, etc., which handle hazardous chemicals, are potential targets for deliberate actions by terrorists, criminals and disgruntled employees. Security risks arising out of these threats are real and must be assessed to determine whether the security measures employed within the facility are adequate or need enhancement. The essential steps involved are threat analysis, vulnerability analysis, security countermeasures, and emergency response. Threat analysis involves the study of identifying sources, types of threats, and their likelihood. Vulnerability analysis identifies the weaknesses in a system that adversaries can exploit. Depending on the threat likelihood and vulnerabilities, various security countermeasures are suggested to improve the plant security. Appropriate emergency response measures that could mitigate the consequences of a successful attack and concepts of inherently safer processes in the light of process security are also discussed in the paper. It is recognised that serious terrorist threats exist to the transport system of hazardous chemicals (by road, rail cars, ships, pipelines, etc.). However, that is not a part of this study, which concentrates on process plants and hazardous materials within immovable boundaries. A case study of a fertiliser plant is used to show the application of ideas presented.

The Bhopal gas tragedy: could it have happened in a developed country?

Abstract The Bhopal gas tragedy occurred in December 1984 wherein approximately 41 tonnes of deadly MIC was released in the dead of night. It caused the death of over 3000 people and continued life-long misery for over 300,000 with certain genetic defects passed on to the next generation. It happened in a plant operated by a multinational, Union Carbide Corporation, in a developing country, India. The tragedy has changed the chemical process industry (CPI) forever. The results have been new legislation with better enforcement, enhancement in process safety, development of inherently safer plants, harsher court judgements, pro-active media and NGOs, rights-conscious public, and a CPI management willing to invest in safety related equipment and training. These have already resulted in savings of several hundred lives and over a billion dollars in accident damages [Kletz, T. (1998a). Process plants: a handbook of inherently safer designs. London: Taylor & Francis. Sutton, I. Chemical Engineering, 106(5), (1999). 114]. However, thousands did not have to die for the world to realise the disaster potential of CPI. The question that still remains is whether such an accident could have happened in a developed country. The answer is ‘yes’, as a number of major accidents in the developed countries since 1984, such as the Piper Alpha oil platform fire (1988, 167 killed), the Zeebrugge ferry disaster (1987, 167 killed), Phillips petroleum fire and explosion (1989, 23 killed), the Challenger disaster (1986, 7 killed), Esso Australia Longford explosion (1998, 2 killed) have demonstrated. One or more of the following are the primary reasons for such disasters: The indifferent attitude of the management towards safety, the lax enforcement of the existing regulations by the regulatory bodies as well as unusual delays in the judicial systems. Such conditions can happen regardless of the level of development in a country. Hence, the Bhopal gas tragedy could have happened in a developed country too, albeit with a lower probability. This paper is concerned with the possibility and not with the probability value. It also points out that further significant advances in process safety will occur with fundamental research into the causes of accidents and with a move towards inherently safer design.

Inherently Safer Design--Present and Future

Inherently Safer Design (ISD) has evoked deep interest in the process industries since the 1990s. Two books and many articles have been written about it and a few specific conferences have been held on the topic. However, its adoption by industry appears to be less than expected. In order to increase its adoption by industry and to make ISD more user friendly, the UK Engineering and Physical Sciences Research Council (EPSRC) has funded a project at Loughborough University. As a first step, we desired to know the status of use of ISD in industry, its teaching and research in academies, and the role of the regulators in its adoption. We also wished to discover the reasons for slow adoption, obtain views on how to increase it and find out about successful applications. To do this, we carried out a survey amongst industrialists, academics and regulators. We enlisted the help of numerous research and trade journals, professional conferences and web sites. 63 completed responses were received from 11 countries representing a whole spectrum, from those who have only recently heard of ISD to those who have practised it successfully for over two decades. Several responders said that they will henceforth start to use ISD. Most were either not familiar with the indices developed for ISD or thought them too complicated. Amongst the reasons cited for limited adoption were: lack of case studies dealing with economic benefits; lack of a tried and tested yet simple methodology of application; lack of desire to change; lack of knowledge about ISD amongst research chemists, engineers, managers and regulators; no enforcing regulation; lack of specific research funds for academics in this area, etc. Tackling these will result in the spread of ISD. Suggestions are made towards achieving this end.

Security risk assessment: Applying the concepts of fuzzy logic

Chemical process industries (CPI) handling hazardous chemicals in bulk can be attractive targets for deliberate adversarial actions by terrorists, criminals and disgruntled employees. It is therefore imperative to have comprehensive security risk management programme including effective security risk assessment techniques. In an earlier work, it has been shown that security risk assessment can be done by conducting threat and vulnerability analysis or by developing Security Risk Factor Table (SRFT). HAZOP type vulnerability assessment sheets can be developed that are scenario based. In SRFT model, important security risk bearing factors such as location, ownership, visibility, inventory, etc., have been used. In this paper, the earlier developed SRFT model has been modified using the concepts of fuzzy logic. In the modified SRFT model, two linguistic fuzzy scales (three-point and four-point) are devised based on trapezoidal fuzzy numbers. Human subjectivity of different experts associated with previous SRFT model is tackled by mapping their scores to the newly devised fuzzy scale. Finally, the fuzzy score thus obtained is defuzzyfied to get the results. A test case of a refinery is used to explain the method and compared with the earlier work.

TWO-DIMENSIONAL SOLIDIFICATION WITH NATURAL CONVECTION IN THE MELT AND CONVECTIVE AND RADIATIVE BOUNDARY CONDITIONS

Two-dimensional solidification in a rectangular enclosure has been analyzed, taking into account the effects of natural convection and considering the convective and radiative boundary conditions at the surface of the mold and at the top of the enclosure. The bottom is taken as insulated. The dimensionless equations governing the unsteady velocity profiles in the melt and the unsteady temperature profiles in the melt, the solid, and the mold are solved by finite-difference methods, using the alternating direction implicit technique for the vorticity and the stream function. The effect of natural convection on the heat transfer at the interface and on the movement and shape of the interface is found to be significant compared to the results obtained by neglecting natural convection in the melt.

Calculation of Fire and Explosion Index (F&EI) value for the Dow Guide taking credit for the loss control measures

Abstract The Dow Fire and Explosion Index (F&EI) is universally used in evaluating the hazard category of a process plant, area of exposure, expected losses in case of fire and explosion, etc. In the current procedure, the effects of the loss control measures (LCMs) on the F&EI value are not taken into account. This makes the plant look more hazardous, makes it more spread out, requires more elaborate emergency measures and alarms the public and the civil administration more than is necessary. It also affects the insurance premium. We suggest taking the effects of the LCMs into account in the F&EI value. We call this the ‘Offset F&EI’ value. It favorably affects all the above items, and other related ones. To do this, we have developed the relevant equations and have proved the efficacy of the Offset F&EI by means of an example.

A new Hazardous Waste Index.

Hazardous wastes, once generated, have to be stored, transported, treated, disposed off, recycled, depending upon the situation. With laws being tightened, all of the above operations have to be done safely without causing harm to people and environment. Before any operation is carried out, it is vital to know the hazardous characteristics of the waste to be handled. Because waste, generally, is a mixture instead of a pure compound, its hazardous characteristics are difficult to determine and generalize because each waste is specific. A new Hazardous Waste Index (HWI) is proposed in this paper. The index measures hazards related to flammability, reactivity, toxicity and corrosivity as well as the pH value for a hazardous waste. Two examples are given for its use. The index can be modified to include radioactive or mixed waste.

Application of DOW's fire and explosion index hazard classification guide to process plants in the developing countries

DOWs Fire and Explosion Index Hazard Classification Guide (DOW Index) has become a standard document in many countries, including several developing countries. The DOW Index, first issued by the DOW Chemical Co. in 1964, was based upon the Factory Mutuals Chemical Occupancy Classification Guide. The latter as well as subsequent revisions of the DOW Index are based primarily on the experiences in the U.S. which, while applicable to other developed countries, will not be applicable to developing countries in toto, due to differences in costs, training, attitudes and regulations. (This is not intended as a criticism of the situation in the developing countries, since many of the developed countries had themselves passed through similar situations in previous years.) Application of the DOW Index as is, therefore, results in lower than realistic values, thus giving a false sense of security than is actually warranted by the situation in hand. Suggested below are changes that should be and can easily be made to take into account the ground realities. Mentioned in separate sections are also a few comments on the recently issued DOW Index, 7th edition, to make it more internationally user-friendly, as well as suggestions to include some more items to make the DOW Index more dynamic.